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Christina Wells and Desmond Layne

We are using a minirhizotron camera system to observe fine root dynamics beneath irrigated and nonirrigated peach trees. Our long term goals are: 1) to relate the timing of fine root production to tree phenology, soil water content, and soil temperature; and 2) to determine how fine root architecture and demography differ between trees with and without supplemental irrigation. In early 2002, minirhizotrons were constructed and installed beneath each of 72 open-center, 4-year-old `Redglobe' peach trees at the Musser Fruit Research Farm near Clemson University. Beginning in May 2002, videotaped images from each minirhizotron were collected at 2-week intervals; notes on tree phenology were also recorded biweekly. Videotapes were digitized in the lab, and information on root length, diameter, appearance and longevity was extracted from the images. Soil temperature and volumetric water content were measured in the orchard throughout the growing season. In the 2 years following minirhizotron installation, irrigated trees allocated a significantly greater percentage of their fine root length to the upper soil layers and exhibited less root branching than nonirrigated trees. Fine roots produced by irrigated trees lived significantly longer: irrigated trees had a median root life span of 165 days, while nonirrigated trees had a median root life span of only 115 days (P< 0.001; proportional hazards regression). Fine roots from irrigated trees remained in the physiologically active “white” state for an average of 10 days longer than roots from nonirrigated trees (P< 0.001). Data from 2002–03 indicate that the trees produce new root flushes at least three times during the year, with a significant flush occurring immediately after harvest.

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P. Eric Wiseman and Christina Wells

Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with numerous landscape tree species and can improve tree growth and environmental stress tolerance. Construction-related soil disturbance is thought to diminish AMF colonization of transplanted trees in newly developed landscapes. We gathered root, soil, and foliar data from red maples (Acer rubrum) growing in newly developed landscape sites and adjacent native forest sites to test the hypotheses that: 1) landscape trees show lower levels of AMF colonization than forest trees; and 2) the AMF inoculum potential of landscape soils is lower than that of forest soils. Fine roots sampled from landscape maples had significantly lower AMF colonization than maples from adjacent forest sites (3% vs. 22%; P= 0.0002). However, soil-sand mixtures made from landscape soils possessed greater AMF inoculum potential than those made from forest soils (10% vs. 4%; P= 0.0081). Forest soils were more acidic and possessed less extractable P than landscape soils, and differences in AMF colonization between forest and landscape maples appeared to reflect differences in soil chemical properties rather than in soil inoculum potential.

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Shann Tanner, Christina Wells, and Gregory Reighard

The effectiveness of soil solarization as an alternative to methyl bromide (MBr) fumigation in replanted peach orchards was investigated at the Musser Fruit Research Farm near Clemson, S.C. A split plot experimental design was used, with soil treatment as the whole-plot factor and rootstock as the sub-plot factor. In Spring 2002, preexisting trees were removed from the study site, and six orchard rows were cultivated and subsoiled. In June, two rows were covered with clear polyethylene sheeting and solarized for the remainder of the summer. In November, two additional rows were treated with MBr (474.3 kg·ha-1), while the two remaining control rows received no soil sterilization treatment. In Jan. 2003, 36 `Redglobe' peach trees budded on Guardian™ or Lovell rootstock were transplanted to the site, and one minirhizotron was installed beneath each tree. Minirhizotron observations were made every 14–21 days from Feb. through Oct. 2003, and stem caliper measurements were taken on four dates during this interval. Trees grew significantly larger in the MBr and solarized rows than in the control rows (P< 0.1; Tukey's hsd), but there were no differences in stem caliper growth between MBr and solarization-treated trees. Reduced aboveground growth in control trees may have been related to greater carbon expenditure belowground: in the absence of soil sterilization, fine root median life spans were reduced by 27–28 days (P< 0.0001; proportional hazards regression) and rates of root production and mortality were significantly higher (P< 0.1; repeated measures ANOVA). Solarization and MBr fumigation appeared to provide similar benefits in reducing root turnover and improving aboveground growth at this site.

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Christina E. Wells and David M. Eissenstat

Fine root lifespan has previously been estimated at 3 to 4 weeks for apple trees growing in England. We used nondestructive belowground imaging technology to investigate the accuracy of this estimate for apple trees growing in central Pennsylvania. Eight root observation tubes (minirhizotrons) were installed beneath each of six 20-year-old `Red Delicious' apple trees on M26 rootstock. Videos of roots growing against the tubes were taken at intervals of 14 to 28 days between October to June, depending on the amount of root activity. Images were used to construct a database of life history information for over 500 individual roots. A flush of fine roots was produced in the early fall, followed by a period of low but constant mortality that lasted through December. Roots that survived to this time were generally maintained throughout the winter and following spring. A second flush of root production occurred in the spring, coinciding with bud burst and flowering. Root mortality was highest in late spring following this flush. In contrast to earlier estimates of apple root lifespan, we found that >30% of the fine roots produced in the fall lived for ≥200 days. Most of these roots developed red-brown pigmentation, a feature that previously has been associated with cortical cell death. However, the ability of these pigmented roots to produce new white laterals in the spring argues against categorizing these as dead roots. The information on root demographics provided by this study adds to our understanding of seasonal carbon and nutrient allocation patterns in apple.

Free access

Guang Zeng, Stanley Birchfield, Christina Wells, and Desmond Layne

Minirhizotrons and specialized camera equipment have been widely adopted for in situ observation of fine root dynamics in horticultural settings. However, the laborious nature of data collection from minirhizotron images limits the number and size of experiments that can reasonably be analyzed. Here we present an algorithm for the automatic detection and measurement of roots in minirhizotron images, including the discrimination of light-colored roots from bright background objects. First, two-dimensional matched filtering and local entropy thresholding are used to produce binarized images from which roots are detected. Next, a strong root classifier based on geometric and intensity features is used to discriminate roots from unwanted background objects. A labeling algorithm identifies each individual root in the image, and root lengths and diameters are measured using Dijkstra's algorithm and the Kimura–Kikuchi–Yamasaki method for obtaining the length of a digitized path. This approach allows us to identify and measure fine roots as individuals, rather than simply measuring the aggregate root length in an image. Experimental results from a collection of 250 peach (Prunus persica) root images demonstrate the effectiveness of the approach. The algorithm is able to detect and measure a variety of roots of different shapes, sizes, and orientations, with a detection rate of 92%, a false–positive rate of 5%, and an average measurement error of 4.1% and 6.8% for length and diameter, respectively. Current work involves improving the efficiency of the algorithm and incorporating it into an application. We are also exploring algorithms for tracking the location of a root over time as it grows darker in color and blends with the surrounding soil.

Free access

Gilbert Miller, Ahmad Khalilian, Jeffrey W. Adelberg, Hamid J. Farahani, Richard L. Hassell, and Christina E. Wells

Delineating the depth and extent of the watermelon [Citrullus lanatus (Thumb.) Matsum. & Nak.] root zone assists with proper irrigation management and minimizes nutrient leaching. The objective of this 3-year field study was to measure root distribution and root length density of watermelon (cv. Wrigley) grafted on two different rootstocks (Lagenaria siceraria cv. ‘FR Strong’ and Cucurbita moschata × Cucurbita maxima cv. Chilsung Shintoza) and grown under three soil moisture treatments. Irrigation treatments tested were: no irrigation (NI), briefly irrigated for fertigation and early-season plant establishment; minimally irrigated (MI), irrigated when soil moisture in top 0.30 m of soil fell below 50% available water capacity (AWC); well irrigated (WI), irrigated when soil moisture in top 0.30 m of soil fell below 15% (AWC). Root length density (RLD) was measured from 75-cm-deep soil cores at two locations three times per growing season and a third location at the end of the season. Cores 1 and 2 sample locations were 15 cm to the side of each plant: Core 1 on the same side as the drip tape and Core 2 on the opposite side. At the end of the season, Core 3 was taken 15 cm outside of the bed in bare ground. RLD was significantly greater in the 0- to 30-cm soil depth and dropped dramatically below 30 cm; it was not significantly affected by irrigation treatment or rootstock. Core 1, next to the drip tape, had greater RLD than Core 2, 30 cm from drip tape, but only at the later sampling dates. Roots were found in Core 3 at all depths, but the RLD was significantly less than that measured in Cores 1 and 2. These findings suggest that the effective root zone depth for watermelon is 0 to 30 cm and that the particular scion/rootstock combinations tested in this study do not differ in root system size or location.

Free access

Brian J. Tucker, Lambert B. McCarty, Haibo Liu, Christina E. Wells, and James R. Rieck

As golfers demand higher quality golf green putting surfaces, researchers continue to seek improved turfgrass cultivars. One such improved cultivar is `TifEagle' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy], which is an improvement over traditional bermudagrass cultivars such as `Tifgreen' and `Tifdwarf' due to its ability to tolerate mowing heights of ≤3.2 mm for extended periods. One observed disadvantage of `TifEagle' is its lack of a deep, dense root system compared to previous bermudagrass cultivars. This field study measured mowing height, N rate, and biostimulant product effects on `TifEagle' rooting. Three mowing heights (3.2, 4.0, and 4.8 mm), three N rates (12, 24, and 48 kg N/ha/week), and two cytokinin-containing commercial biostimulant products (BIO1 and BIO2) were examined. Plant responses measured were root length density (RLD), root surface area (RSA), thatch layer depth (TLD), and turf quality (TQ). Increasing mowing height from 3.2 to 4.0 mm increased RLD by >11%, RSA by >11%, and TQ by >17%. Increasing N rates from 12 to 24 kg N ha-1 week-1 increased RLD by >17%, RSA by >26% and TQ by >16%. No effect on RLD was observed after the first year of biostimulant use, however, after the second year, BIO1 increased RLD by >11% when applied with the lowest rate of N (12 kg N/ha/week). Higher mowing heights (4.8 and 4.0 mm) increased TLD >6% compared to the lowest mowing height (3.2 mm), and higher N rates (48 and 24 kg N/ha/week) increased TLD >3% compared to the lowest N rate (12 kg N/ha/week). Overall, a mowing heights ≥4.0 mm, N rates ≥24 kg N/ha/week, and long-term use of a cytokinins-containing biostimulant had a positive effect on `TifEagle' rooting.

Free access

Christina Wells, Karen Townsend, Judy Caldwell, Donald Ham, E. Thomas Smiley, and Michael Sherwood

Landscape trees are frequently planted with their root collars below grade, and it has been suggested that such deep planting predisposes trees to transplant failure and girdling root formation. The objective of the present research was to examine the effect of planting depth on the health, survival, and root development of two popular landscape trees, red maple (Acer rubrum) and `Yoshino' cherry (Prunus ×yedoensis). Trees were transplanted with their root flares at grade, 15 cm below grade or 31 cm below grade. Deep planting had a strong negative effect on the short-term survival of `Yoshino' cherries. Two years posttransplant, 50% of the 15-cm- and 31-cm-deep planted cherries had died, whereas all the control cherries had survived (P< 0.001; 2). Short-term survival of maples was not affected by planting depth. Deep-planted trees of both species exhibited little fine root regrowth into the upper soil layers during the first year after transplant. Four years posttransplant, control maples had 14% ± 19% of their trunk circumference encircled by girdling or potentially-girdling roots; this number rose to 48% ± 29% and 71% ± 21% for 15-cm- and 31-cm-deep planted maples, respectively (P< 0.01; ANOVA main effect). There were no treatment-related differences in girdling root development in the cherries.

Open access

Jeffery W. Marvin, Robert Andrew Kerr, Lambert B. McCarty, William Bridges, S. Bruce Martin, and Christina E. Wells

Clarireedia jacksonii sp. nov. formerly Sclerotinia homoeocarpa F.T. Bennett, one of the causal agents of dollar spot, is the most widespread pathogen in turfgrass systems. Dollar spot (DS) affects both cool- and warm-season grasses, during a wide range of environmental conditions. Field studies were conducted at Clemson University, Clemson, SC, on a creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds) cv. Crenshaw] putting green for 2 consecutive years from August to October in year 1 and July to September in year 2. The objective of the studies was to evaluate biological control agents (BCAs) and synthetic fungicides at reduced rates for their efficacy controlling dollar spot. Four replications of 1.5 × 1.5-m plots were used in the experimental design. Treatments included the following: Bacillus subtilis (BS); plant extract oils (EO) including clove oil + wintergreen oil + thyme oil; extract of Reynoutria sachalinensis (RS); Bacillus licheniformis (BL); chlorothalonil (CL); and azoxystrobin + propiconazole (AzP). Synthetic fungicides were used at reduced rates in combination with biological control agents, to evaluate curative control efficacy of various combinations. All reduced synthetic programs, except CL + EO, provided acceptable disease severity (≤15%) at the end of year 1 and acceptable (≥7) turfgrass visual quality. Azoxystrobin + propiconazole, CL, AzP + BL, AzP + EO, AzP + BS all provided ≤15% disease severity and ≥7 visual turfgrass quality 14 days after the last application in year 2.